This invention is directed to a printer and, in particular, to a printer especially adapted for use in portable or hand-held electronic calculators which is low in power consumption, small in size and low in noise.
Recently, a demand has arisen for printers which can be used in small electronic calculators, such as hand-held or pocketable electronic calculators, which can be carried around easily. In addition to providing a display panel in which calculation entries and results can be viewed, it is highly desirable that such calculation entries or results be printed on a printing tape for checking and future reference. However, conventional printers are less than completely satisfactory or impractical since they require too much power to operate. It is essential that the power consumption of such printers be reduced so that the printer can operate on small batteries for a long period of time. In addition, the printing mechanism itself must be extremely small sized for incorporation into a portable calculator and have a low noise level.
A variety of suggestions for reducing the size of a printer for use in a portable electronic calculator have been proposed in the art. For example, an ink jet-type printer as described herein, can be manufactured in a sufficiently small size to be used in portable or hand-held electronic calculators. However, a major concern is to reduce the power consumption of such printers so that they can be operated on small batteries which allow the printer to be incorporated into a portable calculator. Small dry cells are preferably used in portable electronic calculators which can be carried in the pocket. It is preferable that at most four dry cells UM-III (14.phi..times.50 l mm) be used to power the portable calculator. However, it would be preferable if two dry cells UM-III or a button type silver dry cell could be used.
Several types of small printers are presently available for use in portable electronic calculators. However, in a drum type printer in a flying system, the power consumption required for printing one character is about thirty milli-Joules at best. In a mechanical-type dot printer, the power consumed is about sixty milli-Joules per character. In a thermal-type dot printer, about sixty milli-Joules per character is required for printing. Assuming for the moment that the power consumed in printing one character is thirty milli-Joules, the period of time during which a conventional standard printer can run is calculated as follows, provided that there are 15 characters (printing positions) in each line, and the printing speed is about two lines per second. When a single nickel-cadmium charge type dry cell UM-III having a charge capacity of 1900 Joules is used, the period of operating time is: ##EQU1## If four dry cells are used, the period of operating time is substantially increased four times to about 2.3 hours. However, this is a considerably short period of time when compared with the 1000 average hours during which a portable electronic calculator using a liquid crystal display alone can run.
It is known that employment of a piezoelectrically-driven ink-on-demand type ink jet system in a printing mechanism greatly increases the period of time during which the printer can run on given power supply due to the relatively low power consumption thereof. If the printing energy of the ink jet is 0.01 milli-Joule/dot and one character is printed by fourteen dots on the average (where a 5.times.7 matrix display is employed), then 0.14 milli-Joules is required to print each character. With this data, the following result is obtained using the same formula as above: ##EQU2## That is, the printer will operate for 125 hours on a single cell if the only power required is to jet the ink. Therefore, if the energy required for operating a printer which translates an ink jet printing mechanism and operates a sheet feeding mechanism can be minimized, then a printer which is lower in power consumption than conventional printers can be realized which can be used in a portable electronic calculator.
The small printers, also referred to as "microprinters", which are presently available on the market consume more than 500 milli-Joules to operate the drive mechanism which moves the printing mechanism across the printing sheet and the sheet feeding mechanism which feeds the printing sheet through the printer. Thus, a small printer which is low in power (energy) consumption has not been provided heretofore.
Moreover, in a battery-driven pocketable electronic calculator having a printer, the printing sheet area in the printer generally occupies a relatively large space and hence the calculator remains bulky. Therefore, it is also desirable that the small printer can use not only a conventional rolled printing tape but also a flat printing sheet (cut sheet) such as a memorandum sheet so that the printer does not require a separate printing tape housing section in order to hold a rolled printing tape.
Where the printer includes a print head on a movable carriage which regularly makes a non-uniform motion with respect to the printing sheet, i.e. the speed of travel is not constant, it is desired to provide a control system for determining the discrete printing positions of the print head so that appropriate printing signals can be supplied thereto for printing in the proper position. In controlling a printer with a carriage which makes a non-uniform motion, it would be desirable to provide a detecting mechanism between the print head carriage and the printer or calculator frame in order to detect in the ratio of 1:1 with respect to the plural printing positions. However, such control is technically difficult if not impossible to achieve where the print head does not have a constant speed. In the case where, as in a dot printer, there are a number of printing positions in a single line, such detection is often impossible and a great deal of energy would be consumed if such a device could be used. Even if such control in the ratio of 1:1 could be achieved, the control mechanism would be very expensive to manufacture.
Accordingly, a small printer especially adapted for use in a portable electronic calculator which is low in power consumption, relatively quiet in operation and which includes a printing position control mechanism, is extremely desired.